Method of producing semiconductive bodies



Dec. 20, 1955 M. SPARKS 2,

METHOD OF PRODUCING SEMICONDUCTIVE BODIES Filed June 15, 1950 ATTORNEY United States PatentO1 2,727,839 METHOD OF PRODUCING SEIVIICONDUCTHVE BGDTES Morgan Sparks, Summit, N. J., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application June 15, 1954], Serial No. 168,182 4 Claims. (Cl. l43-1.5)

This invention relates to the production of semi-conductive elements or bodies and more particularly to methods of the general type disclosed in the application Serial No. 138,354, filed January 13, 1950, of J. B. Little and G. K. Teal, now Patent 2,683,676, granted luly 13, 1954, for producing single crystals of germanium and silicon.

In methods of the general type disclosed in the aboveidentified application, a seed of semiconductive material is partially immersed in a molten mass or" semiconductive material and is then withdrawn therefrom under controlled conditions, at a rate to draw some of the mass along tnerewith whereby an elongated body or rod of the material is produced. in some cases, for example,

as disclosed in the application Serial No. 168,184, filed June 15, 1950, of G. K. Teal, during withdrawal of the seed the conductivity or conductivity type of the molten mass is altered selectively by introducing into the mass a significant impurity, i. e., a donor or acceptor thereby to controllably and selectively alter the electrical characteristics of the portion of the mass withdrawn with the seed at any particular time.

The operating characteristics of semiconductor signal translating devices are dependent markedly upon the quantity and distribution or the significant impurities in the semiconductive material. For example, the resistivity of the body of such material and the characteristics of a junction between the body and a metallic contact thereto vary significantly with the content and concentration of such impurities both in the body and the region at and in the vicinity of the contact. Thus, in the fabrication of semiconductive elements for use in such devices and in the preparation of ingots or large bodies or crystals from which such elements are subsequently cut, it is desirable that the content of impurities be uniform throughout the element or ingot or that the distribution of the impurities vary in a prescribed manner.

One general object of this invention is to improve the quality and uniformity of the product of semiconductive bodies particularly suitable for use in signal translating devices. More specifically, objects of this invention are to facilitate the realization of homogeneous impurity content throughout such bodies or prescribed Zones or regions thereof and to expedite the attainment of a preassigned distribution of the impurities throughout the bodies or such zones or regions.

in accordance with one feature of this invention, in a method of the general type disclosed hereinabove for the production of semiconductive bodies, the molten semiconductive material is caused tofiow through a trough or container past the seed and the impurity conent in the flowing material is controlled to obtain either a homogeneous or preassigned varying impurity content and distribution in the material flowing past the seed being withdrawn. The typeof either the impurity in the molten mass or of the impurity which is in effective excess in the mass may be controlled or altered by inserting into the flowing material upstream from the seed an alloy of the semiconductive material and a significant impurity. For example, the conductivity or conductivity type of a mass initially of N-conductivity type may be altered by introducing thereinto an alloy of the semi- 2,727,839 Patented Dec. 20, 1955 conductive material and an acceptor impurity, thereby to the seed to P-conductivity type. Conversely, if the flowing mass is of P-conductivity type it may be converted to N-conductivity type by introducing thereinto an alloy of the semiconductive material and a donor impurity such as antimony.

The invention and the above-noted and other features thereof will be understood more clearly and fully from the following detailed description with reference to the accompanying drawing in which the single figure is an elevational view, partly diagramamtic, of apparatus illustrative of that which may be utilized in practicing this invention.

Referring now to the drawing, the apparatus therein illustrated comprises a body 1 3, for example of an insulating material such as a ceramic and a bell jar 11 seated upon and sealed to the base 10 and defining therewith a chamber through which a suitable gas, such as hydrogen or helium, may he passed by way of ports 12. Mounted upon the base it by supports 13 is an elongated dish or trough 14 connected at opposite ends to aieservoir l5 and a tank 16 by way of valves 17 and 1?, respectively. The reservoir and tank 15 and 16 an en compassed by heating coils l9 and 249, respectively cou pled to high frequency power sources 21 and 22, rspe tively, whereby the material in the reservoir andtank may be heated as will be described hereinafter.

The tank 16 and reservoir 15 may be connectl by piping 23 and 24 and a suitable circulating devi: 25 to provide a closed circulating system.

Particularly advantageously the trough 14, resvoir l5, tank 16 and the piping and valving associated .erewith are of a material such as carbon which Winot introduce contaminants or impurities into the maria! utilized.

The tank 16 is sealed against the atmosphere anthay be provided with an outlet port 26 leading to a pip, not shown, for purposes which will appear presen.

Mounted adjacent the tank or trough 14 is a rerocable support 27 having afixed thereto a plurali of semiconductor seeds The support 27 may be sed or lowered relative to the tank or trough 14 by a suble mechanism not shown. Also mounted in juxtapdon to the trough 1'4 are a pair of rods 29A and 29B an alloy of the material being operated upon and a sificant impurity, i. e., a donor impurity such as phoorous, arsenic or antimony or an acceptor impuritych as boron, aluminum, gallium or indium. The signint impurity in the two rods 2-9A and 2B may be difnt, that in one rod being a donor and that in the otlan acceptor. The two rods are supported by holdcil) which may be raised or lowered individually with n t to the trough M by a suitable mechanism not shou In the operation of the apparatus, a charge of theirconductive material, specifically germanium or silicof which the elements or crystals are to be drawn is prod in the reservoir 13. Suitable germanium materialy be prepared in the manner disclosed in the applitn Serial No. 638,351, filed December 29, 19 :5, of l. Scafi and H. C. Theuerer, new Patent 2,602,211, gid July 8, 1952 and suitable silicon material for the re may be produced in the manner disclosed in the aption Serial No. 793,744, filed December 24, l947,f.

H. Seat]? and H. C. Theuerer, now Patent 2,561, granted September 18, 1951. The operating chams flushed with an inert gas such as nitrogen and, if dd, a suitable gas such as hydrogen or helium is circi through the chamber through the ports 12. The ch21 the reservoir 15 then is heated through agency of til 19 to liquefy it, and the molten mass is flowed iithrough the trough or dish 14.

The holder 27 islowered to partiallyimmerse theseeds -material will be dependent, of course, upon the significant impurities therein. This may be selectively altered in a controlled manner by introducing either or both of the rods 29A and 2913 into the mass. For example, if the mass is initifly of N-conductivity type, it may be converted to -P-conductivity type by inserting thereinto the rod, say 293, containing acceptor impurities. Conversely, the massif of P-conductivity type may be converted to I i-conductivity type by inserting thereinto the rod, say 29A,..containing the donor impurity. The material withdrawn along with the seeds 28 will, of course, be of the conductivity type of the mass. The conductivity type may be altered one or more times during withdrawal of the scedswhp'reby successive contiguous zones of the drawn rystal'a're of opposite conductivity types and one or more P-N iulctions are produced in the resulting crystals. Rod 29A ould, for example, be of an mloy of 98 per cent germaium and 2 per cent antimony; rod 298 could be 98 per ce't germanium and 2 per cent gallium.

'Aftr passing through the dish or trough 14, the molten materl flows into the tank 16 and there may be heated throng the agency of the coil 20 to vaporize the impurities tlrefrom, the impurities being removed from the tank I the operation of the pump connected to the outlet.26

Thmolten material may be circulated continuously throng the system. Alternatively, the flow of material from c dish or trough 14 may be stopped at any time by closiuthe valve 18, whereby the conductivity and conductiv type of the material withdrawn along with the seedsi will be that of the molten mass in the trough 14 at thaime. As arxample the rate of flow in the trough might be 0.004:ubic centimeter per second for a crystal 1.0 centimeter diameter growing at the rate of 0.002 centimeter per send.

It be noted that flow of the material in the trough or did! eifects a mixing thereof so that homogeneity of coosition of the material withdrawn with the seeds result Thus, uniformity of significant characteristics of the 01818 produced is realized. Further, the volume of molttemiconductive material in the trough or dish 14 may relatively small whereby its conductivity or conducti type may be altered readily, slowly or abruptly.

Slowrnges in the significant impurity content will pro duceresponding gradations in the conductivity of the rystdrawn. Sharp changes in this content are reflectsromptly in the material being withdrawn so that sharN junctions are produced. Similarly, by abrupt alteris in the impurity in efiective excess, thin zones or res of either conductivity type may be produced in thawn crystals, such zones or regions abutting a 'zoneegion of the opposite conductivity type or being betwand contiguous with two zones of the opposite condity type. For example, a thin P zone may be prod between two N zones. Moreover, the volume of shnductor material in the reservoir 15 may be larg'reby a large number of crystals, or crystals of large, or both, may be produced with dispatch.

Agh a specific embodiment of this invention has beeriln and described, it will be understood that it is but ative, and that variousmodilications may be madiein without departingfrom scope and spirit of this :tion.

4 What is claimed is: l. The method of producing a semiconductive body containing a P-N junction therein which comprises introducing a seed into a molten mass of semiconductive ma- 5 terial of one conductivity type and selected from thegroup consisting of silicon and germanium, said seed being of a like material to that of said molten mass, causing the mass to flow laterally past said seed and in contact therewith, withdrawing said seed from said mass at a rate substan- 0 tially equal to the rate of crystallization of the withdrawn material, and, during the withdrawing step, introducing into the molten mass, upstream from said seed an impurity capable of altering the conductivity typeof said mass.

2. The method of producing a semiconductive bodycontaining a PN junction therein, which comprises providing a molten mass consisting essentially of material selected from the group consisting of germanium and silicon and a conductivity type determining impurity, introducing a seed essentially of said material intosaid mass, causing said mass to flow laterally past said seed,'withdrawing said seed from said mass to draw some of said mass along therewith at a rate substantially equal to the crystallization rate of the withdrawn material, introducing into said mass upstream from said seed a conductivity type determining impurity of the type opposite to that in the mass, and continuing the withdrawing step to form a zone in the withdrawn material of conductivity type opposite to that first produced.

3. The method of producing a semiconductive body having a zone of one conductivity type intermediate between zones of opposite conductivity type which comprises providing a molten mass of material selected from the group consisting of germanium and silicon and a first conductivity type determining impurity, introducing a seed of said material into said mass, causing said mass to flow laterally past said seed, withdrawing said seed from said mass to draw some of the massalong therewith .at i

a rate substantially equal to the crystallization rate of the withdrawn material, continuously introducing into said mass upstream from said seed a second conductivity type determining impurityof type opposite to that originally inthe mass for changing the conductivity type of the withdrawn material being crystallized, continuing the withdrawing step to form a zone in the withdrawn mate rialof desired thickness, and substituting for the addition of the second impurity an impurity of type similar to the'first impurity while continuing the withdrawingxstep to form crystalline material of conductivitytype similar to that of the crystalline material first produced.

4. The method of producing a semiconductive body containing a series of PN junctions, formed by introducing into a molten mass consisting essentially of a conductivity type. determining impurity and a material selected from the group consisting of germanium and silicon a seed of like material, causing the mass to flow laterally past said seed and in contact-therewith, alternately introducing into said mass upstream from said seed impuri- I ties of different conductivity types, and withdrawing said 0 seed from said mass at;a rate substantially equal to the rate of crystallization of the withdrawnmaterial, whereby the conductivity type of'the material crystallized changes alternately.

OTHER REFERENCES 1 J. Applied.Physics,,1935, v.6. Pages. 1119116. Preparation of Metal. Single Crystals, American Society for Metal, Preprint No. 35, 1949. Page 4. 

1. THE METHOD OF PRODUCING A SEMICONDUCTIVE BODY CONTAINING A P-N JUNCTION THEREIN WHICH COMPRISES INTRODUCING A SEED INTO A MOLTEN MASS OF SEMICONDUCTIVE MATERIAL OF ONE CONDUCTIVITY TYPE AND SELECTED FROM THE GROUP CONSISTING OF SILICON AND GERMANIUM, SAID SEED BEING OF LIKE MATERIAL TO THAT OF SAID MOLTEN MASS, CAUSING THE MASS TO FLOW LATERALLY PAST SAID SEED AND IN CONTACT THEREWITH, WITHDRAWING SAID SEED FROM SAID MASS AT A RATE SUBSTANTIALLY EQUAL TO THE RATE OF CRYSTALLIZATION OF THE WITHDRAWN MATERIAL, AND, DURING THE WITHDRAWING STEP, INTRODUCING INTO THE MOLTEN MASS, UPSTREAM FROM SAID SEED AN IMPURITY CAPABLE OF ALTERING THE CONDUCTIVITY TYPE OF SAID MASS. 